Import data from JSON or XML feed and create a List in Android

Question

I am trying to make an Android class that creates a List of other apps, for later display, until now I have the following code for creating the List (taken from a google example):

public final class AppList {

public static List<App> list;

public static List<App> setupApp() {
    list.add(buildAppInfo(
            "Browsers",
            "chrome",
            "description",
            "Google Inc.",
            "com.android.chrome",
            "http://...",
            "http://..."
    ));
    list.add(buildAppInfo(
            "Browsers",
            "Firefox",
            "description",
            "Mozilla",
            "com.mozilla.firefox",
            "http://...",
            "http://..."
    ));
    [An so on...]

    return list;
}

private static App buildAppInfo(String category,
                                    String title,
                                    String description,
                                    String developer,
                                    String packageName,
                                    String iconImageUrl,
                                    String bgImageUrl) {
    App app = new App();
    app.setId(App.getCount());
    App.incCount();
    app.setTitle(title);
    app.setDescription(description);
    app.setDeveloper(developer);
    app.setCategory(category);
    app.setIconImageUrl(iconImageUrl);
    app.setBackgroundImageUrl(bgImageUrl);
    app.setPackageName(packageName);
    return app;
    }
}
//From here everything is handled in other activity

I will like instead to load the details dynamically from a web server that I can setup to feed either a JSONArray or an XML and then put that data on the list. For what I was reading I could use Volley, but I am not very experienced in Volley or Java in general (I am just learning in the road) so I don't have to much idea on how to proceed.

From the google developers site I found an example. I was thinking on add something like this:

public final class AppList {

public static List<App> list;

public static List<App> setupApp() {
    /*Json Request*/
    String url = "https://json_url/";
    JsonObjectRequest jsonObjectRequest = new JsonObjectRequest( Request.Method.GET, url, null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    list.add(response);//ADD ITEMS TO LIST HERE
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {

                }
            });

    return list;
}

private static App buildAppInfo(String category,
                                    String title,
                                    String description,
                                    String developer,
                                    String packageName,
                                    String iconImageUrl,
                                    String bgImageUrl) {
    App app = new App();
    app.setId(App.getCount());
    App.incCount();
    app.setTitle(title);
    app.setDescription(description);
    app.setDeveloper(developer);
    app.setCategory(category);
    app.setIconImageUrl(iconImageUrl);
    app.setBackgroundImageUrl(bgImageUrl);
    app.setPackageName(packageName);
    return app;
    }
}

The data received from the server feed should be something like:

buildAppInfo(
            "Browsers",
            "Firefox",
            "description",
            "Mozilla",
            "com.mozilla.firefox",
            "http://...",
            "http://..."
    )
buildAppInfo(
            "Browsers",
            "Firefox",
            "description",
            "Mozilla",
            "com.mozilla.firefox",
            "http://...",
            "http://..."
    )
[...]
//BUT IN JSON FORMAT

My entire approach obviously doesn't work. Can someone please help me to achieve what I need? Thank you.

Answer 1

The simplest set up for what you want to do requires:

A way to read content from a URL, parsing the received JSON array. For example, into a JSONArray or JSONObject (which you can get on mvnrepository):

public static JSONArray parseJsonFromUrl(String uri) throws IOException, JSONException {
    JSONArray array = null;
    try (Scanner sn = new Scanner(new URL(uri).openStream(), "UTF-8")){
      array = new JSONArray(sn.useDelimiter("\\A").next());
    }
    return array;
}

Mapping the received information to a List of specific App objects, e.g.:

public static List<App> getAppList(JSONArray array){
    List<App> appList = new ArrayList<>();
    for (int i = 0; i < array.length(); i++) {
            JSONObject object = array.getJSONObject(i);
            appList.add(buildAppInfo(object.getString("category"), object.getString("title"), object.getString("description"), object.getString("developer"), object.getString("packageName"), object.getString("iconImageUrl"), object.getString("bgImageUrl")));
    }
    return appList;
}

The approach for consuming XML is similar, using an XML parser instead (Check out How to read XML response from a URL in java? for details).

You can use more advanced tools such as Jackson Mapper or Spring RestTemplate for consuming the RESTful service, but I suggest starting with this simple approach until you get more familiar with the Java ecosystem.

[UPDATE]

I've made a quick demo using the code of this answer so you can tinker with it. You can also use it as a boilerplate to build the rest service you need using Spring Boot. (Check out https://elcodedocle-jsontest.herokuapp.com/apps for a live deployment of the latest passed travisCI build of the service)

[ANOTHER_UPDATE]

In case you are still clueless, here is a full android app consuming a list (json array of "app" json objects) served via RESTful service, using the code written on this answer from an android app (Yes, you can import this one as a fully functional android studio project): https://github.com/elcodedocle/android-resttest

Remember this is a basic example using the simplest way I can come up with for a beginner. If you keep coding for a while around the Java ecosystem you will discover more advanced tools that you might find more suitable for your project, once you have enough experience to be able to wrap your head around their correct usage.